The present invention relates to techniques for transferring fluids to and from vessels offshore using and undersea pipe and a buoy supported deliery hoe.
Offshore loading and unloading of fluid tankers, for instance, petroleum tankers, is necessary in the case of certain deep-draft vessels where suitable deep water channels to shore loading and unloading points are unavailable. In addition, much oil exploration and production occurs from underwater drilling at sea. Both of these make it necessary and convenient to transfer fluids and gasses, for example, natural gas, to and from a floating vessel at sea.
In the prior art, it has been customary to anchor a tower-type floating buoy to a sea bed using an anchor plate rigidly secured to the sea bed and attached to the tower by means of a universal joint or cardan joint. A stationary, usually rigid, undersea line leads to the base of the buoy and a flexible line is connected from there up the tower to a transfer point above the surface of the water.
The flexible line is subjected to constant flexure as the tower is moved around by the action of wind, waves and tides and thereby experiences continuous alternation of stress. This makes the flexible lines subject to wear and can cause oil spills upon rupture. In addition, the undersea environment makes inspection and replacement of flexible lines difficult, expensive and dangerous. Furthermore, the weakening of the flexible line due to flexure as previously discussed is accelerated by the strong outside pressure from depths of as much as 100 meters or more.
The problem of wear in flexible undersea lines encountered in transferring liquid or gaseous products is significantly compounded when it is desired to transfer heated or cooled materials. In particular, the transmission of cryogenic temperature products such as liquefied natural gas or ammonia requires substantial insulation to prevent foaming of the material being transferred and/or the freezing of sea water about the lines. The use of flexible lines are incompatible with this requirement.